The thing about Molokini is that you really have to set out in one of the early morning boats, otherwise the trip is bumpy. Also since the OP has kids, I'm not sure they would like to jump off of the boat into 40ft of water, although I admit it is crystal clear. When we went, the operator did a sweep of the island first with a fishing line hanging out, which I gather is illegal. We only had 15min in the water and since the crater wall was about 50 yards from the boat, most of the time was spent swimming to the wall and back. I saw more snorkeling around the beaches on my own schedule but maybe I just had a bad charter at a bad time.